holy seed: and for the same reason, the children of Christians, even when only one of the parents is pious, are accounted holy; and according to the testimony of the apostle, differ from the impure seed of idolaters. "
-Institutes of the Christian Religion (Book IV, Chapter 10)
To mark this distinction, the children of believers were circumcised in Old Testament times and are baptized in New Testament times.
2. God's promise of grace includes children as well as adults. When God sealed His covenant promise with the children of Abraham by giving the sign of circumcision, He proclaimed, "And I will establish My covenant between Me and thee and thy seed after thee in their generations for an everlasting covenant, to be a God unto thee, and to thy seed after thee" (Genesis 17:7).
When God sealed the same covenant promise with the worldwide body of believers -the New Testament seed of Abraham -by instituting the non-bloody sign of baptism, He stated by the Apostle Peter, "For the promise is unto you, and to your children, and to all that are afar off, even as many as the Lord our God shall call" (Acts 2:39).
Peter was preaching here to a Jewish audience from all parts of the world (Acts 2:9-11, 14, 22, and 36). They knew what "the promise" referred to very well. For approximately eighteen hundred years they and their children had been circumcised upon the basis of God's promise. Now Peter states that the New Testament form of the church is to be baptized upon the same promise -"Be baptized everyone of you in the Name of Jesus Christ...for the promise is unto you, and to your children" (Acts 2:38b-39a).
Children of believers were circumcised in the Old Testament upon the same promise which children of believers are baptized upon in the New Testament, i.e., Genesis 17:7.
3. God's church includes children as well as adults. Old Testament references include children as members of God's congregation, e.g., Joshua 8:35, II Chronicles 20:13, Nehemiah 12:43, Joel 2:15-16. Jesus included children and severely admonished His
Pious -Religious; church-attending people
He shall feed His flock like a shepherd: He shall gather the Iambs with His arm, and carry them in His bosom, and shall gently lead those that are with young.
But when Jesus saw it, He was much displeased, and said unto them, Suffer the little children to come unto Me, and forbid them not: for of such is the kingdom of God.
And I will establish My covenant between Me and thee and thy seed after thee in their generations for an everlasting covenant, to be a God unto thee, and to thy seed after thee.